1. Field of the Invention
The present invention relates to a process for producing a 4-formyl-4'-methylbiphenyl, which will be hereinafter referred to as MBPAL, as a precursor of 4, 4'-biphenyldicarboxylic acid.
4, 4'-biphenyldicarboxylic acid (hereinafter referred to as BPDC) which is obtained by oxidation of MBPAL, is a useful raw material for high performance polyester resin or aramide resin having a good heat resistance and a high strength.
2. Related Prior Art
Hitherto, various processes for producing have been proposed for production of BPDC. However, since the so far proposed processes are complicated or provide a low yield, they are actually not economical processes for producing BPDC.
GB 2155921 has proposed a process for producing BPDC which comprises reacting a 4-alkylbiphenyl with carbon monoxide in the presence of a HF-BF.sub.3 catalyst to obtain a 4-alkyl-4'-formylbiphenyl in a high yield and then oxidizing the thus obtained 4-alkyl-4'-formylbiphenyl with a gas containing molecular oxygen.
In the process of GB 2155921, 4-alkyl-4'-formylbiphenyl is obtained in a high yield using 4-alkylbiphenyl as a raw material. However, 4-alkylbiphenyl is not a raw material commercially available in a low price. Accordingly, for example, it is required that a biphenyl is carbonylated to synthesize a 4-formylbiphenyl and then the thus synthesized 4-formylbiphenyl is hydrogenated to produce a 4-methylbiphenyl. In case of producing MBPAL by applying the process according the GB 2155921, since the process requires many reaction steps including carbonylation of biphenyl, recovery of HF-BF.sub.3 catalyst, separation of 4-formylbiphenyl and its hydrogenation, carbonylation of 4-methylbiphenyl and separation MBPAL, the apparatus for production is complicated and an amount for use of utility becomes large.